Complaints about sleep and daytime alertness are common in ESRD patients. Eight consecutive ESRD patients with a sleep complaint were studied with all-night polysomnography. All were found to have significant sleep apnea with a mean apnea/hypopnea index (AHI) of 64 +/- 41.6 episodes per hour of sleep (range 7.5 to 140/hr of sleep). The majority of apneas were of the central or mixed variety causing severe fragmentation of sleep and frequent awakenings. Treatment was attempted with nasal continuous positive airway pressure (NCPAP). NCPAP was highly successful in six of the eight patients, reducing the mean AHI to normal or near normal levels (6.0 +/- 3.8/hr of sleep, P < 0.02 vs. baseline). The quality of sleep was significantly improved with statistically significant decreases in light stage 1 sleep, and nocturnal oxygenation improved with statistically significant increases in low SaO2 values. Five of six responders reported that they awoke feeling more alert and fewer times from sleep. The etiology of sleep apnea in ESRD is unknown although the frequent central apneas suggest a dysfunction of central respiratory control resulting from the effects of renal failure. Sleep-related complaints in patients with ESRD are likely to result from sleep apnea, a sleep disorder that can be diagnosed with polysomnography and treated with NCPAP.